1. Field of the Invention
The present invention relates generally to moving objects and devices for use therewith, and more particularly, to methods and devices for decelerating moving vehicles.
2. Prior Art
Along many highways, exits are provided for runaway trucks or other types of vehicles. Once a vehicle takes such an exit, it enters a stretch of a road that is filled with relatively fine sand of an appropriate depth. As the runaway vehicle enters the sand-filled portion of the road, it quickly begins to decelerate and slow down and after a relatively short distance it comes to rest. The deceleration of the vehicle is caused primarily by the process of “sinking” the vehicle tires into the sand, and forcing it to continuously “climb the height of the sand in front of it, i.e., a height equal to the sinking depth of the tire. The kinetic energy of the vehicle is absorbed primarily by the friction forces generated within the displacing sand. This process is fairly similar to an uphill travel of a vehicle, which would decelerate a non-powered vehicle and eventually bring it to rest. The amount of deceleration, i.e., the rate of slow-down, is dependent on the uphill slope. For the case of a sand-filled road, the amount of deceleration that can be achieved is dependent on the depth of the sand and the mechanical characteristics in terms of the amount of resistance that it can provide to its displacement by the tires.
As the vehicle travels along the sand-filled road, the vehicle usually experiences a fairly bumpy ride, since the sand cannot be made and maintained perfectly flat and perfectly homogeneous or protected from contaminants carried by the wind and rain and also by an uneven absorption of moisture. Another major disadvantage of the sand is that due to the relatively small friction that it provides between the tire and the roadway, the tires can easily skid sideways and slip, particularly if the driver attempts to use the brakes, and the vehicle may easily be rendered minimally controllable while slowing down. As a result, accidents, such as overturning and jackknifing, can occur while the vehicle is being brought to rest. The skidding, slipping and partial loss of control becomes increasingly more probable with increased initial speed of the vehicle as it enters the stretch of sand-filled road.
In addition, a depth of sand that is most appropriate for a certain vehicle weight, number of tires, and/or tire size may not be appropriate for other vehicles having a significantly different weight, number of tires, and/or tire size. For example, a road with a depth of sand that is appropriate for a heavy truck will decelerate a light vehicle too fast and can therefore result in injury to the passengers due to the rapid deceleration and/or most likely due to the vehicle loss of control. The optimal depth of the sand is also dependent on the initial speed of the vehicle. If a vehicle enters the sand-filled road with a relatively slow speed, then it would be best for the depth of sand to be relatively small, so that the vehicle is brought to stop as slowly as the length of the sand-filled road allows. Other factors also contribute to the optimal design of such sand-filled roads such as the weight of the vehicle, the number and size of the tires, etc. In short, to achieve an optimal condition, a sand-filled road has to be tuned to the type of the vehicle, its entering weight and initial velocity. In addition, the road and sand conditions have to be regularly monitored and maintained. Such conditions cannot obviously be met for roads that are constructed for general use and are subject to various environmental conditions. Such sand-filled roads are in use in numerous highways and are particularly located where the downward slope of the road is high and heavier vehicles such as trucks are prone to run away and are used as the means of last resort.
Such sand-filled roads are not, however, suitable for fast moving vehicles such as airplanes. For the case of airplanes, other issues may also arise. For example, the load on each tire is usually much larger than road vehicles; the relative distance between the tires may be smaller than those of road vehicles, thereby rendering them more uncontrollable; the center of mass of the plane may be higher than that of road vehicles, thereby making them more prone to tipping over; etc. In addition, and particularly for fast moving planes, the load applied to the tires keep varying due to the suspensions and the lift action, and therefore may cause a ripple to be formed on the surface of the sand-filled road, thereby making the ride even more bumpy and uncontrollable. In addition, the sand-filled section of the runway needs to be re-leveled after each use. In short, sand-filled roads are not appropriate and practical for fast moving vehicles in general and for airplanes in particular.
To overcome the aforementioned shortcomings for airplanes, runway segments have been added to the end of test runways that are constructed with a special type of concrete that collapses in a more or less controlled manner under the load of the airplane tire. Such runway segments solve some of the aforementioned problems of sand-filled roadways. However, such runway segments leave some of the major aforementioned problems unsolved and they even create some new problems and hazards. For example, the problem of lack of control is only partially solved by reducing the skidding potential caused by the sand. However, the collapsed concrete tends to constrain the tire to travel, more or less, in the generated “groove,” making it difficult for the plane to maneuver (turn) sideways due to the resistance that the uncrushed “concrete wall” provides against the tire as it attempts to turn sideways. In addition, the concrete material cannot be formed such that it is sufficiently homogeneous to prevent bumpy rides. In addition, the collapsible concrete runway can only be optimally formulated and constructed for a certain airplane with a certain total weight and certain initial velocity as it reaches the collapsible segment of the runway.
Furthermore, once the collapsible segment of the runway is used by a “runaway” plane during landing or takeoff, the damaged segment has to be repaired before the runway can be opened to traffic. Otherwise, the damaged segment would pose a hazardous condition for the next runaway plane or even for a plane that could have stopped if a regular runway segment was present in place of the collapsible segment. In addition, while the repair crew is repairing the damage, any takeoff or landing would pose a hazardous condition for the repair crew and the plane. The use of the runway must therefore wait for the completion of the repairs, including the time required for the proper setting of the added or replaced sections of the concrete and inspection of the final condition of the runway. In short, the operation of the airport must be significantly curtailed for a significant length of time, and if the airport has only one runway, the entire operation of the airport has to be suspended until the damaged sections of the collapsible runway has been repaired. In short, such collapsible runway segments have major technical difficulties for safe operation and even those technical problems are one day solved, they are still effectively impractical due to the required relatively long periods of closure after each use and the related economical costs involved.
A need therefore exits for reusable runways and driveways that can slow down or bring to stop a “runaway” vehicle. For high-speed approaches, particularly for airplanes, it is also essential that the ride be as smooth as possible and that the vehicle stays fully controllable during the entire time it is being decelerated. It is also highly desirable that the runway or driveway parameters be readily adjustable to optimally match the type, weight and initial speed of the vehicle. Such adaptable runway segments are particularly important for planes for the aforementioned reasons and in practice, the parameters of the runway segment can be readily adjusted by the air traffic controller or even by the pilot since all the required information about the plane and its flight conditions is known prior to landing and takeoff. The information may even be automatically transmitted from the plane by a wireless means to a central processor. In addition, if the plane is experiencing some type of malfunction or is damaged, the runway segment may be adjusted for optimal performance with each specific condition. Such changes in the runway parameters may be achieved manually or automatically before the plane reaches the runway segment or even as it is traveling along the runway.
Such runway segments may even be placed along the entire length or a portion of the runway (or other road surface) to routinely assist in the deceleration of aircraft (or other vehicles), thereby reducing their tire and brake wear. The equipped runway segments may also be kept inactive, thereby acting as a regular (solid) segment of the roadway surface, and be activated only when needed, such as in an emergency.